Since a centrally located knight has the power to threaten eight other
squares simultaneously, you should always be on the lookout for a possible fork.
A fork, as it relates to chess,
is when you purposely attack more than one piece at a time,
and knights are custom-made for this purpose.
The most crushing of forks is when you check your opponent's king,
attacking his queen as well. Unless your knight can be killed,
you force your adversary to move his king, and on the next move you take the queen.
This is also valuable in king/rook, queen/rook,
or rook/rook combinations, because the other player can't move them both
in only one turn.
Keeping your knights in the central area significantly increases
their flexibility, power, and forking potential.